Ground fault circuit interrupters (GFCIs) are a type of electronic circuit breaker that may be used in some electrical systems to protect an electrical circuit from ground faults. A ground fault may exist when a current imbalance occurs between a power (or hot) conductor and a neutral conductor of an electrical circuit. GFCIs may be used to prevent electrical shock hazards in electrical circuits that are adjacent to water, such as, e.g., in bathrooms and/or kitchens. Upon detection of a ground fault, a trip circuit within the GFCI may be activated to interrupt or disconnect power (i.e., current flow) from an electrical power source to the protected electrical circuit.
To ensure that a GFCI is operating properly, GFCIs may have a self-test feature that automatically checks the functionality of the GFCI at regular intervals, such as, e.g., every two or three hours. During a self test, the trip circuit may be disabled to prevent the GFCI from unnecessarily disconnecting power from the protected electrical circuit. However, a potentially hazardous situation may exist if a large ground fault occurs in the protected electrical circuit at the onset of the self test. That is, the GFCI may not respond to detection of a ground fault until after the self test concludes. Another potentially hazardous situation may also exist if a self-test controller within the GFCI malfunctions by, e.g., outputting a trip circuit disable signal that is stuck at either a logic high level or a logic low level. Such a stuck signal may permanently disable the trip circuit and thus prevent the GFCI from disconnecting power in response to detection of a ground fault.
Accordingly, there is a need for methods and apparatus that disable a trip circuit of a GFCI during a self test and yet still allow the trip circuit to respond during the self test to detection of a large ground fault.